It is generally known for a silver-containing catalyst to be employed in the preparation of ethylene oxide from ethylene. See for example U.S. Pat. No. 3,962,136, issued June 8, 1976 and also the literature cited therein. In order to obtain improved silver cataysts, efforts have been directed for many years towards modifying the silver catalysts with the aid of promoters. For example, the above-mentioned U.S. Pat. No. 3,962,136 describes a process in which a silver compound is applied to a carrier, after which the applied silver compound is reduced to silver and in which additionally a promoter in the form of potassium oxide, rubidium oxide or cesium oxide or a mixture thereof is present on the carrier.
In co-pending application Ser. No. 874,913, filed June 16, 1986 is described a process for the preparation of a silver-containing catalyst suitable for the oxidation of ethylene to ethylene oxide, whereby a silver compound and, if desired, a promoter are applied to an alkali enriched carrier, after which the silver compound is reduced to metallic silver, and in which process the alkali enriched carrier has been prepared by mixing an aluminum compound with a salt of a metal of Group 1A of the Periodic System and by calcining the mixture. The obtained silver catalyst has an improved stability.
An alternative process has been found, wherein alkali enriched carrier has been prepared by mixing a hydroxide of a metal of Group 1A of the Periodic System, especially cesium hydroxide, an organic fluorine compound and an aluminum compound and by calcining the obtained mixture. The carrier is then used in the preparation of silver catalysts with improved stability.
This is surprising since alkali enriched alumina carriers, prepared with alkali metal hydroxides without the addition of an organic fluorine compound, are much less suitable for silver catalysts, since the latter have less stability.